The phosphorylation of glucose to glucose-6-phosphate (G6P) is the initial step in the catabolism of glucose. The direct phosphorylation of glucose by Pi (inorganic phosphate) is described by the equation glucose + Pi ? glucose-6-phosphate + H2O, ?G��= 13.8 KJ/mol a) Calculate the equilibrium constant for the above reaction. In hepatocytes, the physiological concentrations of glucose and Pi are maintained at approximately 4.8 mM. What is the equilibrium concentration of G6P obtained by the direct phosphorylation of glucose by Pi? Does this reaction represent a reasonable metabolic step for the catabolism of glucose? Explain. b) In principle, one way to increase the concentration of G6P is to drive the equilibrium reaction to the right by increasing the intracellular concentrations of glucose and Pi. Assuming a fixed concentration of Pi at 4.8 mM, how high would the intracellular concentration of glucose have to be to give an equilibrium concentration of G6P of 250 ?M? Would this route be physiologically reasonable, given that the maximum solubility of glu7cose is less than 1 M? c) The phosphorylation of glucose in the cell is coupled to the hydrolysis of ATP; that is, part of the free energy of ATP hydrolysis is used to phosphorylate glucose: i) glucose + Pi ? glucose-6-phosphate + H2O, ?G��= 13.8 KJ/mol ii) ATP + H2O ? ADP + Pi, ?G��= -30.5 KJ/mol Sum: glucose + ATP ? glucose-6-phosphate + ADP Calculate K�eq for the overall reaction. For the ATP-dependent phosphorylation of glucose, what concentration of glucose is needed to achieve a 250 ?M intracellular concentration of glucose-6-phosphate when the concentration of ATP and ADP are 3.38 mM and 1.32 mM, respectively? Does this coupling process provide a feasible route for the phosphorylation of glucose in the cell? Explain. d) Although coupling ATP hydrolysis to glucose phosphorylation makes thermodynamic sense, we haven�t yet specified how this coupling takes place. Given that coupling requires a common intermediate, one conceivable route is to use ATP hydrolysis to raise the intracellular concentration of Pi and thus drive the unfavorable phosphorylation of glucose by Pi. Is this a reasonable route? e) The ATP-coupled phosphoryaltion of glucose is catalyzed in hepatocytes by the enzyme glucokinase. This enzyme binds ATP and glucose to form a glucose-ATP-enzyme complex, and the phosphoryl group is transferred directly from ATP to glucose. Explain the advantages for this route.